Zinc, a major soluble component of particulate matter, may be a critical toxic agent in the cardiorespiratory pathophysiologic effects of exposure to atmospheric dusts. Nonetheless, the molecular targets that underlie zinc toxicity within lung remain unknown. We recently reported that extracellular zinc (1-100 ?M) increased amiloride-sensitive sodium currents of heterologously expressed murine epithelial Na+ channel (ENaC) subunits. Since a) ENaC-dependent sodium reabsorption across airway epithelia has a significant role in regulating the volume of airway surface liquids (and hence mucociliary transport); and b) activation of ENaC is essential in the pathogenesis of chronic airway disorders such as cystic fibrosis, we hypothesize that activation of ENaC by zinc is an important molecular determinant of the toxicity of inhaled particulate matter. Accordingly, the specific aims of this proposal are (i) to determine the effects of zinc on ENaC activity and its impact on periciliary liquid (PCL) height, mucociliary transport (MCT) and ciliary beat frequency (CBF) in primary cultures of human bronchial epithelium (HBE); (ii) to determine the effects of zinc on ENaC activity in a heterologous expression system; and (iii) to identify the molecular mechanism by which zinc activates ENaC. Our proposed studies regarding the effects of extracellular zinc on ENaC activity in primary cultures of airway epithelium and in heterologous expression systems will provide fundamental biophysical and molecular information towards our understanding of the pulmonary response to inhaled particulate matter. Our proposed study will examine the link between excess zinc, a suspected major player in human lung injury due to inhaled particulates, and the activity of lung sodium channels that are critical regulators of mucus clearance, the primary lung defense mechanism. This study will enhance our understanding of mechanisms by which atmospheric dusts result in lung damage, and will provide basic information that may lead to the development of intervention measures.